The LOw Frequency ARay (LOFAR) is a multipurpose radio antenna array aimed to detect radio signals in the frequency range 10-240 MHz, covering a large surface in Northern Europe with a higher density in Northern Netherlands. The high number density of radio antennas at the LOFAR core in Northern Netherlands allows to detect radio signals emitted by cosmic ray induced air showers, and to characterize the geometry of the observed cascade in a detailed way.
A study of several geometrical parameters of radio signals emitted by extensive air showers propagating in the atmosphere, and their correlation with the observed radio frequency spectrum in the 30-70 MHz regime is here presented.
In order to find the best parameters which describe the correlation between primary cosmic ray information and the emitted radio signal, a cross-check between real data and simulations has been done. Regarding real data, cosmic ray radio signals detected by LOFAR since 2011 have been analysed. For the simulation of radio signals, the CoREAS code, a plug-in of the CORSIKA particle simulation code, has been used.
Preliminary results on how the frequency spectrum changes as function of distance to the shower axis, and as function of primary particles mass composition are shown.
The final aim of this study is to find a method to infer information of primary cosmic rays in an independent way from the well-established fluorescence and surface detector techniques, in view of affirming the radio detection technique as reliable method for the study of high energy cosmic rays.